Samsung's contribution to the enthusiast flash drive market perhaps deserves special recognition, as its 840 Pro series arrived ahead of the holidays with 21nm Toggle NAND chips and crushed most of the competition. Although it's been a while and OCZ's flagships can certainly put up a fight, we still tend to favor Samsung's product -- at least partly because the 512GB 840 Pro as survived a year of duty in my office PC.

Flash performance and endurance is a tricky subject, but we're confident that the SSD 840 Pro remains one of the best in both categories, so we knew Samsung would really have to step things up. It was only a matter of how, of course, and the company revealed that part at its annual global summit. Having aced its attempts at speed and durability, Samsung seems focused on solving flash's biggest sacrifices: size and affordability.

Its new SSD 840 Evo lineup has models spanning from 120GB to 1TB, with the largest costing only $0.65 per gigabyte thanks to its use of TLC NAND. Meanwhile, the Evo drives promise solid performance courtesy of several ingenious features, including an SLC-based write cache ("TurboWrite") as well as a secondary caching system called RAPID (Real-time Accelerated Processing of I/O Data) that dips into system memory.

Samsung 840 Evo 1TB & 250GB in Detail

To be clear, the SSD 840 Evo is still aimed at performance buffs, while the older SSD 840 Pro series is largely aimed at enthusiasts willing to pay for the best performance. Armed with Samsung's MEX (SATA 3.1) controller, the series comes in five capacities: 120GB ($109), 250GB ($183), 500GB ($370), 750GB ($530) and 1TB ($650). The drives have a slim 2.5" design, measuring 100.08 x 69.85 x 7.11mm and weighing up to 54.4g.

The 120GB model touts read and write speeds of 540MB/s and 410MB/s, which is more than claimed by the same capacity SSD 840 Pro, while the 250GB, 500GB, 750GB and 1TB models can hit 540MB/s and 520MB/s. All of them have Samsung's 19nm 3bpc TLC Toggle DDR 2.0 NAND flash memory. You'll find two of those chips in the 120GB and 250GB versions, four in the 500GB unit and double that again in the 750GB/1TB variants.

TurboWrite -- one of the caching features we mentioned -- helps the Evo's TLC memory deliver MLC-like performance by using a small portion of each TLC NAND die as an SLC write buffer. The 120GB and 250GB Evo drives have a 3GB TurboWrite buffer and that increases by 3GB for each subsequent model with the 1TB having a 12GB buffer.

The idea is to write data to the SLC buffer before quickly moving it to the TLC memory. If you write a file that is larger than the buffer or the buffer becomes full and doesn't clear in time, the data is written directly to the slower TLC memory. For light use the 120GB and 250GB models should be fine, but you might experience a slowdown if you consistently write more than 3GB of data.

For example, the 250GB Evo's sequential write performance is around 500MB/s when using TurboWrite, but that will drop to below 300MB/s if the buffer fills up. This is mostly a non-issue for the 1TB drive because its 12GB buffer should be able to handle most conditions.

The Samsung MEX controller features a triple-core Cortex R4 processor, just like the SSD 840 Pro's MDX except the frequency of its three cores has been increased from 300MHz to 400MHz. SATA 3.1 support is also available, bringing queued TRIM commands -- something we first experienced on the SanDisk Extreme II.

The Evo series can also access up to a gig of system memory with its RAPID DRAM caching feature, which is unique to these drives and supposedly boosts read performance by storing frequently accessed data in your RAM -- something we'll explore in more detail on the next page.

Whereas the SSD 840 Pro series comes in 128GB, 256GB and 512GB models, the Evo range is cut down to 120GB, 250GB and so on to deal with the use of TLC memory. Additionally, each drive is equipped with a healthy cache: 256MB for the 120GB and 250GB drives, 512MB for the 500GB version and a massive 1GB for the 750GB and 1TB models.

Interestingly Samsung is not making claims as to how many terabytes of data can be written before the drives will expire and instead has simply backed them with a three-year warranty.